Purine and Pyrimidine Metabolism

Question 1

Where does the first position (N) in a purine come from?

Answer 1

Aspartate

Question 2

Where does the second position (C) in a purine come from?

Answer 2

N10-formyl-FH4

Question 3

Where does the third position (N) in a purine come from?

Answer 3

Glutamine

Question 4

Where does the fourth (C) , fifth (C) , and 7th positions (N) in a purine come from?

Answer 4

Glycine

Question 5

Where does the sixth position (C) in a purine come from?

Answer 5

CO2

Question 6

Where does the eighth position (C) in a purine come from?

Answer 6

N10-formyl-FH4

Question 7

Where does the ninth position (N) in a purine come from?

Answer 7

Glutamine

Question 8

Where does most de novo purine biosynthesis occur?

Answer 8

the liver

Question 9

How many molecules of ATP are required for de novo purine synthesis?

Answer 9

7

Question 10

What is responsible for converting ribonucleotides to deoxyribonucleotides?

Answer 10

ribonucleotide reductase

Question 11

What are the 4 key enzymes regulated in purine synthesis?

Answer 11

• PRPP synthetase
• amidophosphoribosyl transferase
• adenylosuccinate synthetase
• IMP dehydrogenase

Question 12

What is the rate limiting enzyme in de novo purine nucleotide biosynthesis?

Answer 12

PRPP

Question 13

What do AMP and GMP feedback inhibit?

Answer 13

adenylosuccinate synthase and IMP dehydrogenase respectively

Question 14

What does conversion of IMP to adenylosuccinate en route to AMP require?

Answer 14

GTP

Question 15

What does conversion of XMP to GMP require?

Answer 15

AMP

Question 16

What enzyme converts Adenine to AMP?

Answer 16

adenine phosphoribosyl transferase (APRT)

Question 17

What enzyme converts hypoxanthine to IMP in the purine salvage pathway?

Answer 17

hypoxanthine-guanine phosphoribosyl transferase (HGPRT)

Question 18

What enzyme converts guanine to GMP in the purine salvage pathway?

Answer 18

hypoxanthine-guanine phosphoribosyl transferase (HGPRT)

Question 19

guanine and hypoxanthine are converted to ______ and then to ______ by _______

Answer 19

guanine and hypoxanthine are converted to xanthine and then to uric acid by xanthine oxidase

Question 20

what inhibits xanthine oxidase, thereby decreasing uric acid formation?

Answer 20

allopurinol

Question 21

What are causes of hyperuricemis that are over producers?

Answer 21

• various genetic defects in PRPP synthetase
• enzyme defects such as hypoxanthine-guanine phosphoribosyl transferase
• cancer, chemo

Question 22

What is gout?

Answer 22

a metabolic disorder of purine catabolism

Question 23

Where does gout first manifest?

Answer 23

first metatarsal phalangeal joint

Question 24

What is allopurinol used in ?

Answer 24

tx of gout

Question 25

What are the causes of hypouricemia?

Answer 25

• adenosine deaminase deficiency
• purine nucleoside phosphorylase deficiency
• xanthine oxidase deficiency

Question 26

What is the committed step in pyrmidine synthesis?

Answer 26

formation of carbamoyl aspartic acid (CAA)

Question 27

What is the regulated step in pyrmidine biosynthesis?

Answer 27

formation of cystolic carbamolyic phosphate

Question 28

What do disorders of folate and vitamin B12 metabolism result in?

Answer 28

deficiencies of TMP

Question 29

CPS II is allosterically inhibited by….?

Answer 29

UTP

Question 30

CPS II is activated by…?

Answer 30

PRPP and ATP

Question 31

What are the end products of pyrmidine catabolism?

Answer 31

highly water soluble CO2, NH3, B-alanine, and B-aminoisobutyrate